Membrane electrode assembly

Abstract

To provide a membrane electrode assembly that can suppress the decrease in power generation performance of a fuel cell. [Solution] A membrane electrode assembly for a fuel cell, wherein the membrane electrode assembly comprises a cathode catalyst layer, a solid polymer electrolyte membrane, and an anode catalyst layer in this order, the cathode catalyst layer containing at least a catalyst and a highly oxygen-permeable ionomer, and at least one selected from the group consisting of the cathode catalyst layer, the solid polymer electrolyte membrane, and the anode catalyst layer contains a nitrogen-containing polydentate ligand capable of coordinating with iron ions.

Description

[Technical Field]

[0001] This disclosure relates to a membrane electrode assembly. [Background technology]

[0002] Various studies have been conducted on membrane electrode assemblies (MEAs) for fuel cells, such as those disclosed in Patent Document 1. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] U.S. Patent No. 9172107 [Overview of the project] [Problems that the invention aims to solve]

[0004] Improving the durability of fuel cells is a crucial issue when applying them to commercial vehicles. Patent Document 1 discloses that the durability of fuel cells can be improved by adding nitrogen-containing polydentate ligands to the membrane electrode assembly. However, there is a risk that the nitrogen-containing polydentate ligands may poison the catalyst in the catalyst layer, reducing the power generation performance of the fuel cell.

[0005] This disclosure has been made in view of the above circumstances, and its main purpose is to provide a membrane electrode assembly that can suppress the deterioration of the power generation performance of a fuel cell. [Means for solving the problem]

[0006] In other words, this disclosure includes the following aspects: <1> A membrane electrode assembly for fuel cells, The aforementioned membrane electrode assembly comprises a cathode catalyst layer, a solid polymer electrolyte membrane, and an anode catalyst layer in this order. The cathode catalyst layer comprises at least a catalyst and a highly oxygen-permeable ionomer. The membrane electrode assembly, wherein at least one selected from the group consisting of the cathode catalyst layer, the solid polymer electrolyte membrane, and the anode catalyst layer contains a nitrogen-containing polydentate ligand capable of coordinating with iron ions.

[0007] <2> The high oxygen permeable ionomer is a sulfonyl group-containing polymer, The sulfonyl group-containing polymer includes a structural unit having a sulfonyl group and a structural unit having a cyclic structure, The structural unit having a cyclic structure is at least one of a first structural unit having four functional groups and a second structural unit having five functional groups, In the first structural unit, the four functional groups are each a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms, The membrane electrode assembly according to <1>, wherein in the second structural unit, the five functional groups are each a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms.

[0008] <3> The membrane electrode assembly according to <1> or <2>, wherein the nitrogen-containing polydentate ligand is contained in the anode catalyst layer or the solid polymer electrolyte membrane.

[0009] <4> The catalyst in the cathode catalyst layer contains at least one selected from the group consisting of platinum particles, platinum alloy particles, and composite particles containing platinum as a catalyst metal, according to any one of <1> to <3>.

[0010] <5> The membrane electrode assembly according to any one of <1> to <4>, wherein the nitrogen-containing polydentate ligand is 1,10-phenanthroline.

Advantages of the Invention

[0011] The present disclosure can provide a membrane electrode assembly capable of suppressing a decrease in power generation performance of a fuel cell.

Brief Description of the Drawings

[0012] [Figure 1] Figure 1 shows the synthesis scheme for polymer A. [Figure 2] Figure 2 is a graph showing the nitrogen-containing compounds used in each anode catalyst layer, the nitrogen-containing compounds used in each cathode catalyst layer, and the ions used in each cathode catalyst layer for Examples 1-2 and Comparative Examples 1-3. [Figure 3] Figure 3 is a graph showing the initial performance test results and durability test results for each test cell in Examples 1-2 and Comparative Examples 1-3. [Modes for carrying out the invention]

[0013] This disclosure relates to a membrane electrode assembly for fuel cells, The aforementioned membrane electrode assembly comprises a cathode catalyst layer, a solid polymer electrolyte membrane, and an anode catalyst layer in this order. The cathode catalyst layer comprises at least a catalyst and a highly oxygen-permeable ionomer. The present invention provides a membrane electrode assembly in which at least one selected from the group consisting of the cathode catalyst layer, the solid polymer electrolyte membrane, and the anode catalyst layer contains a nitrogen-containing polydentate ligand capable of coordinating with iron ions.

[0014] The following expressions and definitions of terms apply throughout this specification and the claims unless otherwise specified. "Constituent units" refer to units derived from monomers formed by the radical polymerization of monomers. Constituent units may be units directly formed by polymerization reactions, or they may be units in which a portion of the polymer has been converted to a different structure by processing the polymer. Such processing includes processing to convert precursor groups of ionic groups to ionic groups, ion exchange processing, hydrogen peroxide treatment of the polymer, heating and drying of the polymer in air, an inert gas atmosphere, or under reduced pressure, fluorination to stabilize the polymer, and processing to replace iodine atoms with hydrogen atoms by photo or radical reactions using radical initiators. A "monomer" is a compound that has a polymerization-reactive carbon-carbon double bond. "Ionic group" refers to H + It is a group having monovalent metal cations, ammonium ions, etc. A "precursor group" is a group that can be converted to an ionic group by known treatments such as hydrolysis or acidification. Examples of precursor groups include the -SO2F group. A "fluorine-containing polymer" refers to a polymer that has fluorine atoms bonded to carbon atoms.

[0015] The decrease in power generation performance of fuel cells due to nitrogen-containing polydentate ligands is presumed to be caused by nitrogen-containing compounds such as 1,10-phenanthroline flowing from at least one of the anode catalyst layer and the solid polymer electrolyte membrane into the cathode catalyst layer, poisoning the catalyst via the ionomer in the cathode catalyst layer, and increasing the gas diffusion resistance of the ionomer. According to this disclosure, by using a highly oxygen-permeable ionomer as the ionomer contained in the cathode catalyst layer, catalyst poisoning by nitrogen-containing polydentate ligands can be suppressed, thereby suppressing a decrease in the power generation performance of the fuel cell. It is presumed that catalyst poisoning by nitrogen-containing polydentate ligands is suppressed because the cyclic structure of the highly oxygen-permeable ionomer inhibits the movement of nitrogen-containing polydentate ligands within the cathode catalyst layer. Therefore, according to this disclosure, the durability of the fuel cell can be improved by nitrogen-containing polydentate ligands, and the power generation performance of the fuel cell can be improved by highly oxygen-permeable ionomers.

[0016] The membrane electrode assembly of this disclosure is for use in fuel cells. The membrane electrode assembly comprises a cathode catalyst layer, a solid polymer electrolyte membrane, and an anode catalyst layer, in that order. The membrane electrode assembly contains a nitrogen-containing polydentate ligand (nitrogen-containing compound) that can coordinate with iron ions. The nitrogen-containing polydentate ligand may be contained in at least one selected from the group consisting of a cathode catalyst layer, an anode catalyst layer, and a solid polymer electrolyte membrane. From the viewpoint of suppressing catalyst poisoning in the cathode catalyst layer by the nitrogen-containing polydentate ligand, it may be contained in at least one of the anode catalyst layer and the solid polymer electrolyte membrane, or may be contained in the anode catalyst layer. The nitrogen-containing polydentate ligand may be any one that can coordinate with iron ions, and examples thereof include those represented by the following formulas (1) to (12).

[0017] [Chemical formula]

[0018] [In formulas (1) to (12), R1, R3, and R4 are each H, CH3(CH2) n , CH3(CH2) n O, CF3(CF2) n , CF3(CF2) n O, COOH, PO(OH)2, SO3H, NH2, OH, and the following formula (A)

[0019] [Chemical formula]

[0020] selected from the group consisting of, where X is H, COOH, PO(OH)2, or SO3H, and n is an integer from 0 to 10. Also, R2 is CH3(CH2) n , CH3(CH2) n O, CF3(CF2) n , CF3(CF2) n O, COOH, PO(OH)2, SO3H, NH2, OH, and selected from the group consisting of the above formula (A), where X is H, COOH, PO(OH)2, or SO3H, and n is an integer from 0 to 10.] The nitrogen-containing polydentate ligand may be 1,10-phenanthroline.

[0021] The cathode catalyst layer contains at least a catalyst and a highly oxygen-permeable ionomer, and optionally the nitrogen-containing polydentate ligand described above. The nitrogen-containing polydentate ligand content in the cathode catalyst layer is, for example, 1 to 10 μg / cm³. 2 This may also be the case. The iron ion content in the cathode catalyst layer may be, for example, 0.1 to 2.0 μg / cm³. 2 That's fine.

[0022] High oxygen-permeable ions are polymers containing sulfonyl groups. A sulfonyl group-containing polymer comprises a structural unit having a sulfonyl group and a structural unit having a cyclic structure. The cyclic structural units constitute the highly oxygen-permeable portion in the sulfonyl group-containing polymer. The cyclic structural unit may be at least one of a first structural unit having four functional groups and a second structural unit having five functional groups. The first structural unit consists of four functional groups, each having either a fluorine atom or a perfluoroalkyl group with 1 to 6 carbon atoms. The second structural unit consists of five functional groups, each having either a fluorine atom or a perfluoroalkyl group with 1 to 6 carbon atoms. The constituent unit having a ring structure may be at least one selected from the constituent unit represented by the following formula (u2-1) and the constituent unit represented by the following formula (u2-2). In formula (u2-1), R 1 ~R 4 Each of these is independently a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms. In formula (u2-2), R 5 ~R 10 Each of these is independently either a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms.

[0023] [ka]

[0024] [ka]

[0025] Examples of monomers that constitute the constituent unit represented by formula (u2-1) include the monomers (m21-1) to (m21-7) shown below. Among these, monomer (m21-1) may be used because it is highly effective in further improving the oxygen permeability of the sulfonyl group-containing polymer.

[0026] [ka]

[0027] Examples of monomers that constitute the constituent unit represented by formula (u2-2) include monomer (m22-1) or monomer (m22-2) as shown below. Among these, monomer (m22-1) may also be used due to its ease of synthesis.

[0028] [ka]

[0029] The constituent unit having a sulfonyl group may be of the following formula (u1). In formula (u1), R F1 ha-(CF2CF(CF3O) h -(CF2) i -, where h is an integer between 0 and 3 (inclusive), and i is an integer between 1 and 10 (inclusive).

[0030] [ka]

[0031] The catalyst contains a catalytic metal. Examples of catalytic metals include platinum, ruthenium, iridium, rhodium, palladium, osnium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, lanthanum, cerium, praseodymium, neodymium, samarium, gadolinium, and yttrium, and two or more of these metals may be used. The metal may also be an oxide, nitride, sulfide, or phosphide. The catalyst metal may be at least one selected from the group consisting of platinum particles, platinum alloy particles, and platinum-containing composite particles. Examples of metals other than platinum that are included in platinum alloys and platinum-containing composite particles include ruthenium, iridium, rhodium, palladium, osnium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, lanthanum, cerium, praseodymium, neodymium, samarium, gadolinium, and yttrium, and may contain two or more of these metals. The elemental ratio of metals other than platinum in the platinum alloy is not particularly limited and may range from 0.1 to 50 atm%. The particle size (average particle size) of the catalyst metal particles is not particularly limited and may be between 1 and 100 nm.

[0032] In this disclosure, the average particle size is determined by measuring the particle sizes of 100 to 1000 particles using an electron microscope and taking the average of these measurements.

[0033] The catalyst may contain a support (carrier). The catalyst metal may be supported on a carrier. The average particle size of the primary particles of the carrier may be, for example, 5 to 500 nm. The metal loading ratio of the catalyst metal supported on the carrier is not particularly limited and may be 1-60% or 18-48%. The support may be conductive carbon, oxides, or the like. The carbon may be carbon black (acetylene black, Ketjen black, and furnace black, etc.), activated carbon, graphite, glassy carbon, graphite, graphene, carbon fiber, carbon nanotubes, carbon nitride, carbon sulfide, and carbon phosphide, or a mixture containing at least two of these. The oxide may be titanium oxide, niobium oxide, tin oxide, tungsten oxide, molybdenum oxide, or a mixture containing at least two of these. In the cathode catalyst layer, the mass ratio (I / C) of the highly oxygen-permeable ionomer to the carbon support in the catalyst may be 0.8 to 1.2.

[0034] The catalyst may contain an ionomer. The ionomer may be an ion-exchange polymer, and the ion-exchange group may be an acidic functional group. The acidic functional group may include sulfonic acid and phosphoric acid. The ionomer may be a perfluorocarbon sulfonic acid polymer, an anion-exchange polymer, or a polymer mainly composed of polyether ether ketone and polybenzimidazole. The ionomer may be the high oxygen-permeable ionomer described above.

[0035] Methods for evaluating the weight of the catalyst metal, support, and ionomer contained in a catalyst include thermogravimetric analysis (TG) and radio frequency inductively coupled plasma emission spectroscopy (ICP).

[0036] The anode catalyst layer contains at least a catalyst and an ionomer, and optionally the nitrogen-containing polydentate ligand described above. The nitrogen-containing polydentate ligand content in the anode catalyst layer is, for example, 1 to 10 μg / cm³. 2 The iron ion content in the anode catalyst layer may be, for example, 0.1 to 2.0 μg / cm³. 2 That's fine. The catalyst contained in the anode catalyst layer may be the same as, or different from, the catalyst contained in the cathode catalyst layer described above. The ionomer may be the high-oxygen-permeable ionomer described above, or it may be an ionomer other than the high-oxygen-permeable ionomer. Examples of ionsomers other than the high-oxygen-permeable ionomer include those similar to the ionomers included in the catalyst described above. In the anode catalyst layer, the mass ratio (I / C) of the ionomer to the carbon support may be 0.8 to 1.2.

[0037] Examples of solid polymer electrolyte membranes include fluorine-based electrolyte membranes such as thin films of perfluorosulfonic acid containing water, and hydrocarbon-based electrolyte membranes. The solid polymer electrolyte membrane may also be, for example, a Nafion membrane (manufactured by DuPont). The solid polymer electrolyte membrane contains the nitrogen-containing polydentate ligands described above, if necessary. The nitrogen-containing polydentate ligand content in the solid polymer electrolyte membrane is, for example, 1 to 10 μg / cm³. 2 The iron ion content in the solid polymer electrolyte membrane may be, for example, 0.1 to 2.0 μg / cm³. 2 That's fine.

[0038] [Catalyst layer formation method] Methods for forming the catalyst layer include, for example, a method that involves the following catalyst ink preparation step and catalyst ink coating step.

[0039] [Catalyst ink preparation process] First, a predetermined amount of a carrier supporting a catalyst metal (catalyst metal-supported carrier), a highly oxygen-permeable ionomer or an ionomer other than a highly oxygen-permeable ionomer, a solvent, and, if necessary, a nitrogen-containing compound are added to a container. These are then stirred using a stirrer to prepare the catalyst ink. The solvent is not particularly limited, and any liquid can be used, including water, alcohol, or a mixed solution of at least one alcohol and water. Examples of alcohols include methanol, diacetone alcohol, ethanol, 1-propanol, 2-propanol, tert-butyl alcohol, ethylene glycol, and propylene glycol. Examples of agitators include ultrasonic homogenizers, jet mills, bead mills, ball mills, high-shear mills, and film mixers. The stirring conditions, such as stirring speed, stirring time, and rotation speed, are not particularly limited and can be set as appropriate. Afterward, vacuum degassing may be performed. There is no limit to the standing time; it can be set arbitrarily, and it may be left standing for a day. It is also possible to use it without standing. Furthermore, vacuum degassing may be performed again.

[0040] [Catalyst ink coating process] The prepared catalyst ink is coated onto a substrate, and the solvent is removed after coating. For example, the catalyst ink is coated onto a substrate such as polytetrafluoroethylene (PTFE), and the coated catalyst ink is heated to dry and remove the solvent. The coating method can be any method that allows for uniform coating of the catalyst ink onto the substrate, and examples include die coating, spin coating, screen printing, doctor blade method, squeegee method, spray coating, and applicator method. The heating rate and heating time can be appropriately set depending on the type of solvent, etc. In addition, the removal rate may be increased by degassing at the same time as heating. The coating film thickness may be 5 to 30 μm. The platinum content of the coating film should be 0.1 to 0.6 mg / cm³. 2 The catalyst ink may be applied to satisfy the following conditions. [Examples]

[0041] [High oxygen permeability ionomer synthesis] Based on Japanese Patent Publication No. 2013-216811 and Macromolecule 1993, 26, 5829-5843, polymer A, a highly oxygen-permeable ionomer, was synthesized using perfluoro-2-ethyl-1,3-dioxole (PED), which constitutes the highly oxygen-permeable portion, according to the synthesis scheme of polymer A shown in Figure 1.

[0042] [Polymer A synthesis] PED (5.07 g) and perfluorosulfonyl fluoride vinyl ether (PSVE-A) (28.79 g) were mixed. The molar ratio of PED to PSVE-A was PED:PSVE-A = 0.74:0.26. 0.05 mol% polymerization initiator was added to this mixture. Freeze-degassing and nitrogen purging were repeated three times, and the mixture was allowed to react at room temperature for two days. After that, unreacted monomers were removed by heating under vacuum at 120°C for one hour. This yielded 7.0 g of the target high-oxygen-permeable ionomer (polymer A). The ion exchange capacity of polymer A at this time was 810. The ion exchange capacity of polymer A was calculated using the following method.

[0043] [Ion exchange capacity of fluorine-containing polymer (polymer A)] In a polycarbonate container, 1.0 g of polymer A and 10 mL of a water / methanol mixture containing sodium hydroxide at a concentration of 0.35 N were added and allowed to stand at 60°C for 40 hours to convert the -SO2F groups of polymer A to -SO3Na groups. The solution was back-titrated with 0.1 N hydrochloric acid using phenolphthalein as an indicator to determine the amount of sodium hydroxide in the solution, thereby calculating the ion exchange capacity of the -SO3H type polymer of polymer A. This ion exchange capacity was defined as the ion exchange capacity of polymer A.

[0044] (Examples 1-2, Comparative Examples 1-3) [Fabrication of the cathode catalyst layer] The catalyst particles constituting the cathode catalyst layer have a peak pore size of 3.5 nm, a mesopore volume of 14.0 cc / g with a pore size of 2-30 nm, and a BET specific surface area of ​​708.0 m². 2 A platinum-supported carbon catalyst was used at a concentration of / g. As the ionomer solution, Aquivon® D79-25BS (manufactured by Sigma-Aldrich) was used in Comparative Examples 1 and 2. In Example 1 and Comparative Example 3, an ionomer solution containing polymer A, a highly oxygen-permeable ionomer, water, and ethanol was used. In Example 2, an ionomer solution containing polymer A, a highly oxygen-permeable ionomer, 1,10-phenanthroline as a nitrogen-containing compound, water, and ethanol was used. Catalyst particles were dispersed in the ionomer solutions of Examples 1-2 and Comparative Examples 1-3 using a bead mill to prepare the respective catalyst inks of Examples 1-2 and Comparative Examples 1-3.

[0045] The mass ratio of water to alcohol in each catalyst ink in Examples 1-2 and Comparative Examples 1-3 was set to 1. This catalyst ink was coated onto a polytetrafluoroethylene sheet and dried to prepare a cathode catalyst layer. In Example 2, the nitrogen-containing compound content in the cathode catalyst layer was 6 μg / cm³. 2 The iron ion content is 1.0 μg / cm³. 2 That's what I decided. The Pt basis weight of each cathode catalyst layer in Examples 1-2 and Comparative Examples 1-3 was 0.2 mg / cm³. 2 That's what I decided. The mass ratio (I / C) of ionomer to carbon in the cathode catalyst layers of Examples 1-2 and Comparative Examples 1-3 was set to 1.0.

[0046] [Fabrication of the anode catalyst layer] As a catalyst, platinum-supported carbon catalyst particles (TEC10E30E, 30% platinum-supported carbon, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) were used. In Example 1 and Comparative Example 2, an ionoma solution containing water, ethanol, an aqueous solution of iron nitrate, and 1,10-phenanthroline as a nitrogen-containing compound was used. In Example 2, Comparative Example 1, and Comparative Example 3, an ionoma solution containing water, ethanol, and an aqueous solution of iron nitrate was used. The prepared platinum-supported carbon catalyst particles were dispersed in the ionomer solutions of Examples 1-2 and Comparative Examples 1-3 using a bead mill to prepare the respective catalyst inks for Examples 1-2 and Comparative Examples 1-3. These catalyst inks were coated onto polytetrafluoroethylene sheets and dried to produce the respective anode catalyst layers for Examples 1-2 and Comparative Examples 1-3. In Example 1 and Comparative Example 2, the nitrogen-containing compound content in each anode catalyst layer was 6 μg / cm³. 2 The iron ion content is 1.0 μg / cm³. 2 That's what I decided. The Pt basis weight of each anode catalyst layer in Examples 1-2 and Comparative Examples 1-3 was 0.1 mg / cm³. 2 That's what I decided. The mass ratio (I / C) of ionomer to carbon in the anode catalyst layers of Examples 1-2 and Comparative Examples 1-3 was set to 1.0.

[0047] [MEA preparation] The cathode catalyst layers and anode catalyst layers of Examples 1-2 and Comparative Examples 1-3 were thermally transferred to both sides of a Nafion® film (NR211) to produce the respective film electrode assemblies (MEAs) of Examples 1-2 and Comparative Examples 1-3. The thermal transfer conditions were 140°C and 50 kgf / cm². 2 The test was conducted at 4.90 MPa for 5 minutes. The electrode area for performance evaluation was 1 x 1 cm (1 cm 2 ), 3.6 x 3.6 cm (12.96 cm) for durability evaluation. 2 This MEA was sandwiched between water-repellent paper diffusion layers (GDL) to prepare test cells for Examples 1-2 and Comparative Examples 1-3. Figure 2 is a graph showing the nitrogen-containing compounds used in each anode catalyst layer, the nitrogen-containing compounds used in each cathode catalyst layer, and the ions used in each cathode catalyst layer for Examples 1-2 and Comparative Examples 1-3.

[0048] [Initial performance evaluation] Each of the membrane electrode assemblies in Examples 1-2 and Comparative Examples 1-3 (electrode area: 12.96 cm²) 2 Cell evaluation was performed using each test cell, including the one specified in the example. Current-voltage characteristics were evaluated under low humidity conditions (cell temperature 80°C, humidity 30%RH), and the result was 1.0 A / cm². 2 and 0.05 A / cm 2 The performance (voltage) was measured. The sweep speed for evaluating the current-voltage characteristics was set to 20 mA / s, and the results were obtained by anode sweep. The cell pressure was 150 kPa, the anode gas type was hydrogen, the anode gas flow rate was 1.0 L / min, the cathode gas type was air, and the cathode gas flow rate was 2.0 L / min. The results are shown in Figure 3.

[0049] [High-potential holding test] Each test cell in Examples 1-2 and Comparative Examples 1-3 (electrode area: 12.96 cm²) 2 Using a low-humidity environment (cell temperature 95°C, humidity 30%RH) and low current density (0.2A / cm²), where electrolyte membrane degradation is likely to occur, this method is used. 2 A 300-hour durability test was conducted under the following conditions: cell pressure of 150 kPa, anode gas type of hydrogen with an anode gas flow rate of 1.0 L / min, cathode gas type of air with a cathode gas flow rate of 2.0 L / min. After the durability test, hydrogen / air was supplied, and the current density was 0.05 A / cm² under the same conditions as the initial performance test described above. 2 The characteristics of a polymer electrolyte fuel cell were evaluated, and the rate of change of the cell voltage after a predetermined period of operation compared to the cell voltage at the start of operation (0.05 A / cm² after durability test) was evaluated. 2 Cell voltage at initial performance evaluation: 0.05 A / cm 2 The cell voltage (×100) was measured. The results are shown in Figure 3.

[0050] [Evaluation Results] Figure 3 is a graph showing the initial performance test results and durability test results for each test cell in Examples 1-2 and Comparative Examples 1-3. As shown in Figure 3, the cells in Examples 1 and 2 have a current of 1.0 A / cm². 2 and 0.05 A / cm 2 In the initial performance tests, it was found that the voltage was higher in all cases than in comparative examples 1-3. As shown in Figure 3, the cells of Examples 1 and 2 exhibited a durability test result of 0.05 A / cm² higher than that of Comparative Examples 1 and 3. 2 It can be seen that the rate of change in voltage after durability is small compared to the initial state (high performance retention rate).

Claims

1. A membrane electrode assembly for fuel cells, The aforementioned membrane electrode assembly comprises a cathode catalyst layer, a solid polymer electrolyte membrane, and an anode catalyst layer in this order. The cathode catalyst layer comprises at least a catalyst and a highly oxygen-permeable ionomer. A membrane electrode assembly comprising at least one selected from the group consisting of the cathode catalyst layer, the solid polymer electrolyte membrane, and the anode catalyst layer, wherein the cathode catalyst layer contains a nitrogen-containing polydentate ligand capable of coordinating with iron ions.

2. The aforementioned highly oxygen-permeable ionomer is a sulfonyl group-containing polymer, The aforementioned sulfonyl group-containing polymer comprises a structural unit having a sulfonyl group and a structural unit having a cyclic structure. The aforementioned cyclic structural unit is at least one of a first structural unit having four functional groups and a second structural unit having five functional groups. The first structural unit is a perfluoroalkyl group in which each of the four functional groups is either a fluorine atom or has 1 to 6 carbon atoms. The film electrode assembly according to claim 1, wherein the second structural unit comprises five functional groups, each of which is either a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms.

3. The membrane electrode assembly according to claim 1, wherein the nitrogen-containing polydentate ligand is contained in the anode catalyst layer or the solid polymer electrolyte membrane.

4. The film electrode assembly according to claim 1, wherein the catalyst in the cathode catalyst layer includes at least one selected from the group consisting of platinum particles, platinum alloy particles, and composite particles containing platinum as a catalytic metal.

5. The membrane electrode assembly according to claim 1, wherein the nitrogen-containing polydentate ligand is 1,10-phenanthroline.

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